Re: [HACKERS] EXPLAIN ANALYZE output weird for Top-N Sort

2014-11-14 Thread Jeremy Harris
On 14/11/14 00:46, Simon Riggs wrote: Limit (cost= rows=20 width=175) (actual time= rows=20 loops=1) - Sort (cost= rows=568733 width=175) (actual time= rows=20 loops=1) Sort Method: top-N heapsort Going off on a tangent, when I was playing with a merge-sort

Re: [HACKERS] EXPLAIN ANALYZE output weird for Top-N Sort

2014-11-14 Thread Tom Lane
Jeremy Harris j...@wizmail.org writes: On 14/11/14 00:46, Simon Riggs wrote: Limit (cost= rows=20 width=175) (actual time= rows=20 loops=1) - Sort (cost= rows=568733 width=175) (actual time= rows=20 loops=1) Sort Method: top-N heapsort Going off on a tangent, when I was

Re: [HACKERS] EXPLAIN ANALYZE output weird for Top-N Sort

2014-11-14 Thread Jeremy Harris
On 14/11/14 14:54, Tom Lane wrote: Jeremy Harris j...@wizmail.org writes: On 14/11/14 00:46, Simon Riggs wrote: Limit (cost= rows=20 width=175) (actual time= rows=20 loops=1) - Sort (cost= rows=568733 width=175) (actual time= rows=20 loops=1) Sort Method: top-N heapsort

[HACKERS] EXPLAIN ANALYZE output weird for Top-N Sort

2014-11-13 Thread Simon Riggs
Limit (cost= rows=20 width=175) (actual time= rows=20 loops=1) - Sort (cost= rows=568733 width=175) (actual time= rows=20 loops=1) Sort Method: top-N heapsort The Sort estimate shows 568733 rows, whereas the actual rows are 20. Both are correct, in a way. The node

Re: [HACKERS] EXPLAIN ANALYZE output weird for Top-N Sort

2014-11-13 Thread Tom Lane
Simon Riggs si...@2ndquadrant.com writes: Limit (cost= rows=20 width=175) (actual time= rows=20 loops=1) - Sort (cost= rows=568733 width=175) (actual time= rows=20 loops=1) Sort Method: top-N heapsort The Sort estimate shows 568733 rows, whereas the actual rows

Re: [HACKERS] EXPLAIN ANALYZE output weird for Top-N Sort

2014-11-13 Thread David G Johnston
Tom Lane-2 wrote Simon Riggs lt; simon@ gt; writes: Limit (cost= rows=20 width=175) (actual time= rows=20 loops=1) - Sort (cost= rows=568733 width=175) (actual time= rows=20 loops=1) Sort Method: top-N heapsort The Sort estimate shows 568733 rows, whereas

Re: [HACKERS] EXPLAIN ANALYZE output weird for Top-N Sort

2014-11-13 Thread Tom Lane
David G Johnston david.g.johns...@gmail.com writes: Tom Lane-2 wrote [ shrug... ] The estimated value is the planner's estimate of what would happen *if you ran the node to completion*, which in practice doesn't happen because of the LIMIT. I don't see how a sort node cannot run to